The conventional contact process for the manufacture of sulfuric acid includes burning or combusting molten sulfur in air or other oxygen-containing gas in the combustion chamber of a sulfur furnace to produce a combustion gas comprising sulfur dioxide, oxidizing the sulfur dioxide produced in one or more catalytic oxidation stages of a converter to produce a conversion gas comprising sulfur trioxide, and absorbing the sulfur trioxide in aqueous sulfuric acid to form additional sulfuric acid product.
In order to prepare the sulfur for combustion, it is typically liquefied and fed under pressure through one or more sulfur guns or lances directed into the combustion chamber of a sulfur furnace supplied with combustion air or other oxygen-containing gas. The sulfur lance produces atomized sulfur particles that are discharged into the combustion chamber as a spray of sulfur droplets. Most conventional sulfur lances operate hydraulically to produce an atomized spray of sulfur particles. That is, atomization is achieved by passing the liquefied sulfur under pressure through the nozzle of the lance into the combustion chamber of the furnace without the aid of an atomizing gas. Typically, hydraulic atomization produces a spray of atomized sulfur droplets having an average particle size or diameter in excess of 300 μm or more and containing particles as large as 2000 μm or more. With these large particle sizes, it is difficult to ensure sufficiently rapid vaporization and combustion of the liquid sulfur particles within the combustion chamber volume. Moreover, hydraulically-operated sulfur lances sometimes suffer from the emission of insufficiently atomized liquid sulfur (i.e., “drool”) from the nozzle of the lance. As a result of these deficiencies, unburned sulfur sometimes deposits outside the intended combustion zone within the sulfur furnace, particularly in smaller sulfur furnace installations or during times of turndown when the sulfur pressure is reduced, leading to process inefficiency and increased maintenance requirements.
As an alternative to hydraulic atomization, it has been proposed to pneumatically atomize liquid sulfur utilizing an atomizing gas such as air (See, for example, U.S. Pat. No. 5,807,530 (Anderson); and Conroy et al., Combustion of Sulfur in a Venturi Spray Burner, Industrial & Engineering Chemistry, Vol. 41, No. 12, pp. 2741-2748 (1949)). Anderson, for example, discloses the pneumatic atomization of molten sulfur to an average particle size on the order of about 10 μm utilizing an atomizing sulfur gun fed with sulfur and atomizing air. In order to ensure an adequate retention time of the spray of atomized sulfur particles in the combustion zone, the apparatus of Anderson further includes a concentric combustor and windbox arrangement that imparts a vertical flow of combustion air from the windbox that converges at the nozzle of the atomizing sulfur gun. The sulfur gun of Anderson includes the atomizing nozzle assembly described in U.S. Pat. No. 4,728,036 (Bennett et al.) in which sulfur and air flows are mixed in and passed through a single narrow annular divergent frustoconical passage to produce a spray of atomized liquid sulfur particles discharged into the combustion chamber of the furnace.
Although the teachings of Anderson are significant, the disclosed apparatus is somewhat complex and difficult to integrate in an existing plant. Furthermore, pneumatic atomization of sulfur-containing liquids to an average particle size of 10 μm represents a significant operational cost. That is, despite the purported improvement in rapid vaporization, combustion and lower deposition of unburned sulfur, overall process economics are still hampered to some extent by the attendant power requirements. Moreover, the nozzle design employed in the sulfur gun of Anderson is susceptible to blockage of the narrow annular passage through which the spray of atomized sulfur is emitted by solid contaminants often found in molten sulfur contained in sulfur pits used in commercial sulfuric acid manufacturing operations.
Accordingly, a need persists for effective techniques and apparatus for producing atomized sulfur combustion mixtures that ensure sufficiently rapid vaporization and complete combustion within the design combustion chamber volume to minimize deposition of unburned sulfur in the sulfur furnace, while also improving the overall economics of both the initial capital cost of equipment and the on-going operational costs.